It is known in the audio/video electronics arts to interconnect a variety of consumer electronic processing devices on a bus structure, so that signal available at one device may be utilized by another device connected on the bus. For example audio/video signal available from a television receiver may be applied to a video cassette recorder for storage, or the audio from a television receiver may be applied to a component stereo system for reproduction etc. Examples of this type of audio/video interconnect systems may be found in U.S. Pat. Nos. 4,575,759; 4,581,664; 4,647,973; and 4,581,645.
The signals distributed in these analog bus systems are relatively self contained. That is they include all the timing information necessary for the respective devices connected to the bus to decode the respective signals.
Currently there are a number of compressed audio and video transmission systems, such as the Grand Alliance HDTV system proposed for terrestrial high definition television broadcasting, or the DirecTV.TM. system which currently broadcasts compressed NTSC signal via satellite. Both systems transmit program material in transport packets, and transport packets for different programs and/or program components may be time division multiplexed in a common frequency band. Respective packets undergo noise detection/correction encoding prior to transmission and after reception, and the transport packets are thereafter reconstituted in a receiver. Recording apparatus (e.g. VCR or video disc) and authoring apparatus (e.g. cameras or camcorders) for compressed signals, on the other hand, may process the compressed signals in the same packet format, however they may not require the same noise processing. As a consequence the conveyance of signal between processing components is most conveniently effected in packet form.
Problems arise in communicating compressed signals between processing components if the packetized format is subjected to timing variations or perturbations. Such timing variations may result when one of the processing components is a recording device. A first problem results from the fact that synchronization indicia is not included in all transport packets of compressed data. A further problem results from the non-uniform generation or delivery rate of transport packets which is not suited to recording directly. In addition, a digital recording system may benefit from a continuous signal presence in order to simplify data clock recovery techniques. Furthermore, to facilitate the reproduction of compressed data suitable for decoding may require a suitable timing reference be included during recording, and a relatively precise timing reference for use during reproduction. A recorded timing indicia may facilitate the elimination of data timing perturbations and discontinuities resulting from record/replay processing and enable the recorded signal timing to be restored to that existing prior to recording.